Row unit for agricultural implement

ABSTRACT

An agricultural row unit for use with a towing frame hitched to a tractor includes an attachment frame adapted to be rigidly connected to the towing frame, a linkage pivotably coupled to the attachment frame, and a row unit frame having a leading end pivotably coupled to the linkage to permit vertical pivoting movement of the row unit frame relative to the attachment frame. A hydraulic cylinder coupled to the attachment frame and the linkage, for urging the row unit frame downwardly toward the soil, includes a movable ram extending into the cylinder, and a hydraulic-fluid cavity within the cylinder for receiving pressurized hydraulic fluid for advancing the ram in a direction that pivots the linkage and the row unit frame downwardly toward the soil. An accumulator positioned adjacent to the hydraulic cylinder has a fluid chamber containing a diaphragm, with the portion of the chamber on one side of the diaphragm being connected to the hydraulic-fluid cavity in the hydraulic cylinder, and the portion of the chamber on the other side of the diaphragm containing a pressurized gas.

CROSS-REFERENCE AND CLAIM OR PRIORITY TO RELATED APPLICATION

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 14/824,480, filed Aug. 12, 2015, now allowed, whichis a continuation of and claims priority to U.S. patent application Ser.No. 13/772,053, filed Feb. 20, 2013, now U.S. Pat. No. 9,192,089, whichis a continuation of U.S. patent application Ser. No. 12/882,627, filedSep. 15, 2010, now U.S. Pat. No. 8,544,397, each of which is herebyincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to agricultural implements and,more particularly, to an agricultural row unit for use with agriculturalimplements such as planting row units.

BACKGROUND

As an agricultural planter row unit travels across fields with variablesoil types, soil moisture, residue levels and topography, it isdifficult to maintain constant seed depth and other parameters due tochanging conditions which would ideally require varying the row unitdown force pressure. For example, farming with higher residue levelsalso requires higher row unit down force levels as row cleaners,coulters and other attachments require applied force to keep them in theground and at consistent depths.

At the same time, in many locations there are immoveable rocks or otherobstructions at or below the soil surface which require the planter rowunit to be able to quickly and freely (without undue increase in the rowunit down force) rise up and over the obstruction freely and thenquickly move back down, leaving a minimum amount of the row unplanted.All this must be accomplished at ground speeds of 6 mph or more. Today'splanters typically include many individual row units, at times up to 120ft wide, each of which may be encountering rocks etc. or have a need tofloat up or down independently.

Traditionally springs have been used to urge row units downward.Recently air bag systems have been used to overcome some of thedrawbacks to air spring systems. Air systems provide a more uniform downforce through the vertical range of travel, compared to springs, and aresomewhat easier to adjust than springs. However due to thecompressibility of air and the relatively large volumes required,changes in air pressure are very cumbersome and not adaptable to veryfast change and response to in-cab controls on the go. Air bag systemstypically have a very large cross-sectional area in relation to the hosefeeding the air spring with pressure, which can provide a largemultiplication of force and allow for relatively good isolation of onerow unit relative to another. However, air bag systems typically do notallow for rapid change of the force being applied, because of the largevolume of the air spring in relation to the cross section of the hosesupplying the air.

Prior attempts to use devices such as combination spring/hydraulic shockabsorbers do not provide ready adjustment on the go and tend to increasein force when rapidly striking a foreign object such as a rock requiringthe row unit to quickly rise and come back down to resume planting. Thisincrease in force levels can cause damage to the planter row unitcomponents.

Some previous down-force systems use a spring and a hydraulic cylinderin series. In these systems the hydraulic cylinder does not directlycontrol row unit down force, but rather is used to vary the amount ofspring pressure applied to each unit.

Other systems use hydraulics with a central accumulator. However, withthe accumulator separated from the force creating cylinder, pressurespikes can develop when hitting obstructions such as a rock at highspeed since oil must be forced through hoses or tubes to the remotelylocated accumulator. This is especially problematic on planters having50 or more row units.

As computers and GPS systems have allowed crop production to be managedin a location-specific way as an implement moves through the field, ithas become necessary to achieve more rapid changes in the setting oradjustment of the implement. In the case of a planter row unit, it isalso necessary to generate a large amount of force. Each individualplanter row unit must be able to react to the soil it encountersindependently of the other row units.

An air spring can allow for remote adjustment of the planter downpressure without stopping the forward motion of the implement, which isinefficient. Mechanical springs have historically required that theoperator stop the implement, get out of the tractor, and make a manualadjustment. The slow rate at which an air spring system can be inflatedor deflated means that even if a GPS system determines that a changeneeds to be made because of a programmed or sensed change in the localsoil composition or conditions, by the time the pump can change the airpressure the implement has already moved too far forward of where thechange needed to be made. This forces the average grid size in whichactive adjustments of the planter down pressure can be made to be quitelarge.

SUMMARY

In one embodiment, an agricultural row unit for use with a towing framehitched to a tractor includes an attachment frame adapted to be rigidlyconnected to the towing frame, a linkage pivotably coupled to theattachment frame, and a row unit frame having a leading end pivotablycoupled to the linkage to permit vertical pivoting movement of the rowunit frame relative to the attachment frame. At least a furrow-formingdevice is mounted on the row unit frame. A hydraulic cylinder coupled tothe attachment frame and the linkage, for urging the row unit framedownwardly toward the soil, includes a movable ram extending into thecylinder, and a hydraulic-fluid cavity within the cylinder for receivingpressurized hydraulic fluid for advancing the ram in a direction thatpivots the linkage and the row unit frame downwardly toward the soil. Anaccumulator positioned adjacent to the hydraulic cylinder has a fluidchamber containing a diaphragm, with the portion of the chamber on oneside of the diaphragm being connected to the hydraulic-fluid cavity inthe hydraulic cylinder, and the portion of the chamber on the other sideof the diaphragm containing a pressurized gas.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of the invention may best be understood by reference tothe following description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a perspective view of a planting row unit attached to a towingframe.

FIG. 2 is a partially sectioned side elevation of the planting row unitof FIG. 1 with the linkage that connects the row unit to the towingframe in a level position.

FIG. 3 is the same side elevation shown in FIG. 1 but with the linkagetilted upwardly to move the row unit to a raised position.

FIG. 4 is the same side elevation shown in FIG. 1 but with the linkagetilted downwardly to move the row unit to a lowered position.

FIG. 5 is a top plan view of the hydraulic cylinder and accumulator unitincluded in the row unit of FIGS. 1-4.

FIG. 6 is a vertical section taken along line 6-6 in FIG. 5.

FIG. 7 is a side elevation of the unit shown in FIGS. 5 and 6 connectedto a pair of supporting elements, with the support structures and theconnecting portions of the hydraulic cylinder shown in section.

FIGS. 8A and 8B are enlarged cross sectional views of the supportingstructures shown in section in FIG. 7.

FIG. 9 is an enlarged perspective of the right-hand end portion of FIG.1 with a portion of the four-bar linkage broken away to reveal themounting of the hydraulic cylinder/accumulator unit.

FIG. 10 is a schematic diagram of a first hydraulic control system foruse with the row unit of FIGS. 1-9.

FIG. 11 is a schematic diagram of a second hydraulic control system foruse with the row unit of FIGS. 1-9.

FIG. 12 is a diagram illustrating one application of the hydrauliccontrol system of FIG. 11.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

Although the invention will be described in connection with certainpreferred embodiments, it will be understood that the invention is notlimited to those particular embodiments. On the contrary, the inventionis intended to cover all alternatives, modifications, and equivalentarrangements as may be included within the spirit and scope of theinvention as defined by the appended claims.

Turning now to the drawings, a planting row unit 10 includes afurrow-opening device for the purpose of planting seed or injectingfertilizer into the soil. In the illustrated embodiment, thefurrow-opening device is a V-opener 11 formed by a pair of conventionaltilted discs depending from the leading end of a row unit frame 12. Itwill be understood that other furrow-opening devices may be used. Aconventional elongated hollow towing frame 13 (typically hitched to atractor by a draw bar) is rigidly attached to the front frame 14 of aconventional four-bar linkage assembly 15 that is part of the row unit10. The four-bar (sometimes referred to as “parallel-bar”) linkageassembly 15 is a conventional and well known linkage used inagricultural implements to permit the raising and lowering of toolsattached thereto.

As the planting row unit 10 is advanced by the tractor, the V-opener 11penetrates the soil to form a furrow or seed slot. Other portions of therow unit 10 then deposit seed in the seed slot and fertilizer adjacentto the seed slot, and close the seed slot by distributing loosened soilinto the seed slot with a pair of closing wheels 16. A gauge wheel 17determines the planting depth for the seed and the height ofintroduction of fertilizer, etc. Bins 18 a and 18 b on the row unitcarry the chemicals and seed which are directed into the soil. Theplanting row unit 10 is urged downwardly against the soil by its ownweight, and, in addition, a hydraulic cylinder 19 is coupled between thefront frame 14 (also referred to herein as “front bracket”) and thelinkage assembly 15 to urge the row unit 11 downwardly with acontrollable force that can be adjusted for different soil conditions.The hydraulic cylinder 19 may also be used to lift the row unit off theground for transport by a heavier, stronger, fixed-height frame that isalso used to transport large quantities of fertilizer for applicationvia multiple row units.

The hydraulic cylinder 19 is shown in more detail in FIGS. 5 and 6.Pressurized hydraulic fluid from the tractor is supplied by a hose 20 toa port 21 that leads into a matching port 22 of a housing 23 that formsa cavity 24 of a hydraulic cylinder containing a ram 25. The housing 23also forms a side port 26 a that leads into cavity 26 b that contains agas-charged hydraulic accumulator 27. The lower end of the cavity 24 isformed by the top end surface of the ram 25, so that the hydraulicpressure exerted by the hydraulic fluid on the end surface of the ram 25urges the ram downwardly (as viewed in FIG. 6), with a force determinedby the pressure of the hydraulic fluid and the area of the exposed endsurface of the ram 25. The hydraulic fluid thus urges the ram 25 in anadvancing direction (see FIG. 4).

As can be seen most clearly in FIG. 9, the hydraulic cylinder 19 and theaccumulator 27 are mounted as a single unit on the front frame 14, withthe lower end of the ram 25 connected to a crossbar 30 that is joined atone end to a vertical link 31. The upper and lower ends of the link 31are pivotably attached to upper and lower links 15 a and 15 b,respectively, on one side of the four-bar linkage 15. The other end ofthe crossbar 30 is angled upwardly and pivotably attached to the upperlink 15 c on the opposite side of the four-bar linkage 15. With thismounting arrangement, retracting movement of the ram 25 into the cavity24 tilts the linkage assembly 15 upwardly, as depicted in FIG. 3,thereby raising the row unit. Conversely, advancing movement of the ram25 tilts the linkage assembly 15 downwardly, as depicted in FIG. 4,thereby lowering the row unit.

The accumulator 27 includes a diaphragm 28 that divides the interior ofthe accumulator into a hydraulic-fluid chamber 29 a and a gas-filledchamber 29 b, e.g., filled with pressurized nitrogen. FIG. 2 shows theram 25 in a position where the diaphragm 28 is not deflected in eitherdirection, indicating that the pressures exerted on opposite sides ofthe diaphragm are substantially equal. In FIG. 3, the ram 25 has beenretracted by upward movement of the row unit, and the diaphragm 28 isdeflected downwardly by the hydraulic fluid forced into the accumulator27 by the retracting movement of the ram 25. In FIG. 4, the ram 25 hasbeen moved to its most advanced position, and the diaphragm 28 isdeflected upwardly by the air pressure as hydraulic fluid flows from theaccumulator into the cavity 24. The use of this compact hydraulicdown-force unit with an integral accumulator on each row unit providesthe advantages of quick response and remote adjustability of a hydraulicdown-force control system. If an obstruction requires quick movement,oil can flow quickly and freely between the force cylinder and theadjacent accumulator.

As can be seen in FIG. 4, advancing movement of the ram 25 is limited byengagement of stops 41, 42 on the lower links of the four-bar linkage15, with the row unit frame 12. This prevents any further advancement ofthe ram 25. Advancing movement of the ram 25 expands the size of thecavity 24 (see FIG. 4), which causes the diaphragm 28 in the accumulator27 to deflect to the position illustrated in FIG. 4 and reduce theamount of hydraulic fluid in the accumulator 27. When the ram 25 is inthis advanced position, the row unit is in its lowermost position.

In FIG. 3, the ram 25 has been withdrawn to its most retracted position,which can occur when the row unit encounters a rock or otherobstruction, for example. When the ram 25 is in this retracted position,the row unit is in its uppermost position. As can be seen in FIG. 3,retracting movement of the ram 25 is limited by engagement of stops 41,on the lower links of the four-bar linkage 15, with the row unit frame12.

Retracting movement of the ram 25 reduces the volume of the cavity 24(see FIG. 3), which causes a portion of the fixed volume of hydraulicfluid in the cylinder 19 to flow into the chamber 29 a of theaccumulator 27, causing the diaphragm 28 to deflect to the positionillustrated in FIG. 3. This deflection of the diaphragm 28 into thechamber 29 b compresses the gas in that chamber. To enter the chamber 29a, the hydraulic fluid must flow through a port 32 in the top of theaccumulator 27, which limits the rate at which the hydraulic fluid flowsinto the accumulator. This controlled rate of flow of the hydraulicfluid has a damping effect on the rate at which the ram 25 retracts oradvances, thereby avoiding sudden large movements of the moving parts ofthe row unit, including the V-opener 11.

When the external obstruction causing the row unit 10 to rise iscleared, the combined effects of the pressurized gas in the accumulator27 on the diaphragm 28 and the pressure of the hydraulic fluid returnthe ram 25 to a lower position. This downward force on the V-opener 11holds it in the soil and prevents uncontrolled bouncing of the V-opener11 over irregular terrain. The downward force applied to the V-opener 11can be adjusted by changing the pressure of the hydraulic fluid suppliedto the cylinder 19.

As can be seen in FIGS. 5 and 6, the single unitary housing 23 formsboth the cavity 26 b that contains the accumulator 27 and the cavity 24of the hydraulic cylinder 19 and the fluid passageway 24 that connectsthe cavity 24 of the hydraulic cylinder 19 to the cavity 27 of theaccumulator. By integrating the hydraulic cylinder 19 and theaccumulator 27 in a single housing, there is no relative motion possiblebetween the cylinder 19 and the accumulator 27, with minimal possibilityfor fluid passageways to act like orifices. The cylinder 19 and theaccumulator 27 remain in fixed positions relative to each otherregardless of the movements of the planter row unit via the linkageassembly 15. In this way the upward motion of the ram 25 that occurswhen the planter row unit rolls over an obstruction is directlyconverted into compression of the gas in the accumulator 27 withoutrestriction. It also allows the accumulator 27, which is by definitionan energy storage device, to be mounted in a fully enclosed and safehousing. The accumulator 27 can be securely mounted to avoid puncture orrapid discharge (if it comes loose), or damage from hitting another partof the implement or a foreign object. The integrated cylinder andaccumulator is also a convenient single package for installation andreplacement and minimizes the number of hydraulic hoses and adapters(potential leakage points).

FIGS. 7, 8A and 8B illustrate in more detail how the illustrativehydraulic cylinder/accumulator unit is attached to the front frame 14and the linkage assembly 15. The top of the unitary housing 23 forms astem 41 that projects upwardly through a hole 51 in a bracket 50 (alsoreferred to herein as “support bracket”) attached to the front frame 14.The outer surface of the stem 41 is threaded to receive a nut 52 thatconnects the housing 23 to the bracket 50. The hole 51 is oversized anda rubber washer 52 a is installed on the stem 41 between the nut 52 andthe bracket 50 to allow a limited amount of tilting movement of thehousing relative to the bracket 50. At the base of the stem 41, beneaththe bracket 50, the housing 23 forms a shoulder 42 that engages a curvedbearing ring 53 that also engages a mating lower surface of a washer 54.Thus, the housing 23 can be tilted relative to the axis of the hole 51,with the shoulder 42 sliding over the lower surface of the bearing ring53.

A similar arrangement is provided at the lower end of the ram 25, wherea stem 60 extends downwardly through a hole 61 in the crossbar 30 thatis pivotably attached to the linkage assembly 15. A nut 62 is threadedonto the stem 60 to connect the ram to the crossbar 30. The hole 61 isoversized and a rubber washer 62 a is installed on the stem 60 betweenthe nut 62 and the crossbar 30 to allow a limited amount of tiltingmovement of the ram 25 relative to the crossbar 30. Above the crossbar30, a flange 63 on the ram 25 forms a curved conical surface 64 thatengages a mating surface of a curved bearing ring 65 that also engages amating upper surface of a washer 66. Thus, the ram 25 can be tiltedrelative to the axis of the hole 61, with the flange 63 sliding over theupper surface of the bearing ring 65.

The use of a hydraulic system permits on-the-go adjustments to be madevery rapidly because the hydraulic fluid is incompressible and thereforeacts more directly than an air system. In addition, hydraulic fluidstypically operate at higher pressures, which allows for greater changesin applied forces. The accumulator 27 allows the fluid system to flexand float with the changing terrain and soil conditions. The accumulator27 is preferably centrally mounted so that when any single row unitmoves over an obstruction, the down-pressure cylinder 19 moves todisplace the hydraulic fluid along a common set of lines connecting allrow units. The gas in the accumulator is compressed at the same time,allowing for isolation among the row units so that upward movement ofone row unit does not cause downward movement of other row units.Although the illustrative hydraulic ram is single-acting, it is alsopossible to use a double-acting ram, or a single-acting ram incombination with a return spring.

Another advantage of the compact hydraulic cylinder/accumulator unit isthat it can conveniently mounted to the same brackets that are providedin many row units for mounting an air bag, to control the down pressureon the row unit. For example, in FIG. 9, the brackets 50 and 51 on whichthe hydraulic cylinder/accumulator is mounted are the brackets that areoften connected to an air bag, and thus the same row unit can be usedinterchangeably with either an air bag or the hydrauliccylinder/accumulator to control the down pressure on the row unit.

FIG. 10 is a schematic of a hydraulic control system for supplyingpressurized hydraulic fluid to the cylinders 19 of multiple row units. Asource 100 of pressurized hydraulic fluid, typically located on atractor, supplies hydraulic fluid under pressure to a valve 101 viasupply line 102 and receives returned fluid through a return line 103.The valve 101 can be set by an electrical control signal Si on line 104to deliver hydraulic fluid to an output line 105 at a desired constantpressure. The output line is connected to a manifold 106 that in turndelivers the pressurized hydraulic fluid to individual feed lines 107connected to the ports 71 of the respective hydraulic cylinders 19 ofthe individual row units. With this control system, the valve 101 isturned off, preferably by a manually controlled on/off valve V, afterall the cylinders 19 have been filled with pressurized hydraulic fluid,to maintain a fixed volume of fluid in each cylinder.

FIG. 11 is a schematic of a modified hydraulic control system thatpermits individual control of the supply of hydraulic fluid to thecylinder 19 of each separate row unit via feed lines 107 connected tothe ports 71 of the respective cylinders 19. Portions of this systemthat are common to those of the system of FIG. 10 are identified by thesame reference numbers. The difference in this system is that eachseparate feed line 107 leading to one of the row units is provided witha separate control valve 110 that receives its own separate controlsignal on a line 111 from a controller 112. This arrangement permits thesupply of pressurized hydraulic fluid to each row unit to be turned offand on at different times by the separate valve 110 for each unit, withthe times being controlled by the separate control signals supplied tothe valves 110 by the controller 112. The individual valves 110 receivepressurized hydraulic fluid via the manifold 106, and return hydraulicfluid to a sump on the tractor via separate return line 113 connected toa return manifold 114 connected back to the hydraulic system 100 of thetractor.

FIG. 12 illustrates on application for the controllable hydrauliccontrol system of FIG. 11. Modern agricultural equipment often includesGPS systems that enable the user to know precisely where a tractor islocated in real time. Thus, when a gang of planting row units 120 towedby a tractor 121 begins to cross a headland 122 in which the rows 123are not orthogonal to the main rows 124 of a field, each planting rowunit 120 can be turned off just as it enters the headland 122, to avoiddouble-planting while the tractor 121 makes a turn through the headland.With the control system of FIG. 11, the hydraulic cylinder 19 of eachrow unit can also be separately controlled to turn off the supply ofpressurized hydraulic fluid at a different time for each row unit, sothat each row unit is raised just as it enters the headland, to avoiddisrupting the rows already planted in the headland.

One benefit of the system of FIG. 11 is that as agricultural planters,seeders, fertilizer applicators, tillage equipment and the like becomewider with more row units on each frame, often 36 30-inch rows or 5420-inch rows on a single 90-foot wide toolbar, each row unit can floatvertically independently of every other row unit. Yet the following rowunits still have the down force remotely adjustable from the cab of thetractor or other selected location. This permits very efficientoperation of a wide planter or other agricultural machine in varyingterrain without having to stop to make manual adjustment to a largenumber of row units, resulting in a reduction in the number of acresplanted in a given time period. One of the most important factors inobtaining a maximum crop yield is timely planting. By permitting remotedown force adjustment of each row unit (or group of units), includingthe ability to quickly release all down force and let the row cleanerquickly rise, e.g., when approaching a wet spot in the field, one cansignificantly increase the planter productivity or acres planted perday, thereby improving yields and reducing costs of production.

On wide planters or other equipment, at times 90 feet wide or more andplanting at 6 mph or more forward speeds, one row unit must often riseor fall quickly to clear a rock or plant into an abrupt soil depression.Any resistance to quick movement results in gouging of the soil or anuncleared portion of the field and, thus, reduced yield. With the rowunit having its own hydraulic accumulator, the hydraulic cylinder canmove quickly and with a nearly constant down force. Oil displaced by orrequired by quick movement of the ram is quickly moved into or out ofthe closely mounted accumulator which is an integral part of each rowunit. The accumulator diaphragm or piston supplies or accepts fluid asrequired at a relatively constant pressure and down force as selectedmanually or automatically by the hydraulic control system. By followingthe soil profile closely and leaving a more uniform surface, thetoolbar-frame-mounted row unit permits the planter row unit followingindependently behind to use less down force for its function, resultingin more uniform seed depth control and more uniform seedling emergence.More uniform seedling stands usually result in higher yields than lessuniform seedling stands produced by planters with less accurate rowcleaner ground following.

The term row unit refers to a unit that is attached to a towing frame ina way that permits the unit to move vertically relative to the towingframe and other units attached to that same towing frame. Most row unitsare equipped to form, plant and close a single seed furrow, but rowunits are also made to form, plant and close two or more adjacent seedfurrows.

It will be evident to those skilled in the art that the invention is notlimited to the details of the foregoing illustrated embodiments and thatthe present invention may be embodied in other specific forms withoutdeparting from the spirit or essential attributes thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

The invention claimed is:
 1. A downforce control system for a planterrow unit, comprising: a downforce actuator associated with the planterrow unit to urge the row unit downwardly with a controllable force thatcan be adjusted, said planter row unit producing a gauge wheel downforceduring planting operations, said downforce actuator disposed to changesaid gauge wheel downforce when actuated; a control module for defininga desired gauge wheel downforce; a valve in fluid communication withsaid downforce actuator for adjusting the fluid pressure supplied tosaid actuator, said valve associated with the planter row unit; and acontroller for adjusting the gauge wheel downforce produced by saiddownforce actuator.
 2. The downforce control system of claim 1, whereinsaid row unit is one of a plurality of row units each generating a gaugewheel downforce during planting operations and wherein said downforceactuator and said valve are each one of a plurality of downforceactuators and valves, each of which is associated with one of saidplurality of row units.
 3. The downforce control system of claim 2,wherein each of said plurality of valves adjusts a pressure in one ofsaid plurality of downforce actuators in order to adjust said gaugewheel downforce.
 4. The downforce control system of claim 3, furtherincluding a load sensor associated with one of said plurality of rowunits, said load sensor disposed to measure said gauge wheel downforce,said load sensor in electrical communication with said controller. 5.The downforce control system of claim 3, wherein said valve adjusts apressure in said downforce actuator.
 6. The downforce control system ofclaim 1, further including a transport position detector, whereby whensaid transport position detector detects that said planter row unit isin a transport position, said downforce actuator is prevented fromactuating.
 7. The downforce control system of claim 6, wherein saidclosed-loop feedback circuit includes a control module for inputtingsaid desired gauge wheel downforce Fd.